如何在Postgres数据库中保存一个图像文件?[英] How to save a image file on a Postgres database?

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问题描述

出于学习目的,我正在使用Python+Flask创建一个网站.我想从数据库中恢复图像并在屏幕上显示.但是一次一步.

首先,我不知道如何将图像保存在数据库中.我的搜索仅显示我必须在数据库中使用bytea类型.然后,我得到我的图像,并以某种方式将其转换为一个字节数组(bytea ==位位数?

我能够在Java中发现(也许)如何在Java(

推荐答案

我通常不会为人们编写完整的示例程序,但是您并不需要它,这是一个非常简单的程序,所以您可以去:

#!/usr/bin/env python3

import os
import sys
import psycopg2
import argparse

db_conn_str = "dbname=regress user=craig"

create_table_stm = """
CREATE TABLE files (
    id serial primary key,
    orig_filename text not null,
    file_data bytea not null
)
"""

def main(argv):
    parser = argparse.ArgumentParser()
    parser_action = parser.add_mutually_exclusive_group(required=True)
    parser_action.add_argument("--store", action='store_const', const=True, help="Load an image from the named file and save it in the DB")
    parser_action.add_argument("--fetch", type=int, help="Fetch an image from the DB and store it in the named file, overwriting it if it exists. Takes the database file identifier as an argument.", metavar='42')
    parser.add_argument("filename", help="Name of file to write to / fetch from")

    args = parser.parse_args(argv[1:])

    conn = psycopg2.connect(db_conn_str)
    curs = conn.cursor()

    # Ensure DB structure is present
    curs.execute("SELECT 1 FROM information_schema.tables WHERE table_schema = %s AND table_name = %s", ('public','files'))
    result = curs.fetchall()
    if len(result) == 0:
        curs.execute(create_table_stm)

    # and run the command
    if args.store:
        # Reads the whole file into memory. If you want to avoid that,
        # use large object storage instead of bytea; see the psycopg2
        # and postgresql documentation.
        f = open(args.filename,'rb')

        # The following code works as-is in Python 3.
        #
        # In Python 2, you can't just pass a 'str' directly, as psycopg2
        # will think it's an encoded text string, not raw bytes. You must
        # either use psycopg2.Binary to wrap it, or load the data into a
        # "bytearray" object.
        #
        # so either:
        #
        #   filedata = psycopg2.Binary( f.read() )
        #
        # or
        #
        #   filedata = buffer( f.read() )
        #
        filedata = f.read()
        curs.execute("INSERT INTO files(id, orig_filename, file_data) VALUES (DEFAULT,%s,%s) RETURNING id", (args.filename, filedata))
        returned_id = curs.fetchone()[0]
        f.close()
        conn.commit()
        print("Stored {0} into DB record {1}".format(args.filename, returned_id))

    elif args.fetch is not None:
        # Fetches the file from the DB into memory then writes it out.
        # Same as for store, to avoid that use a large object.
        f = open(args.filename,'wb')
        curs.execute("SELECT file_data, orig_filename FROM files WHERE id = %s", (int(args.fetch),))
        (file_data, orig_filename) = curs.fetchone()

            # In Python 3 this code works as-is.
            # In Python 2, you must get the str from the returned buffer object.
        f.write(file_data)
        f.close()
        print("Fetched {0} into file {1}; original filename was {2}".format(args.fetch, args.filename, orig_filename))

    conn.close()

if __name__ == '__main__':
    main(sys.argv)

用Python 3.3编写.使用Python 2.7要求您读取文件并转换为buffer对象或使用大对象函数.转换为Python 2.6及以上需要安装ArgParse,可能是其他更改.

如果要测试运行,您需要将数据库连接字符串更改为适合系统的东西.

如果您正在使用大图像,请考虑使用 psycopg2 psycopg2的大对象支持而不是bytea - 尤其是lo_import用于存储,lo_export用于直接写入文件,而大的对象读取功能,用于一次读取图像的小块.

其他推荐答案

我希望这对您有用.

import Image
import StringIO
im = Image.open("file_name.jpg") # Getting the Image
fp = StringIO.StringIO()
im.save(fp,"JPEG")
output = fp.getvalue() # The output is 8-bit String.

stringio image

其他推荐答案

import psycopg2
import sys

def readImage():
    try:
        fin = open("woman.jpg", "rb")
        img = fin.read()
        return img

    except IOError, e:
        print "Error %d: %s" % (e.args[0],e.args[1])
        sys.exit(1)

    finally:
        if fin:
            fin.close()
try:
    con = psycopg2.connect(database="testdb", user="abc")
    cur = con.cursor()
    data = readImage()
    binary = psycopg2.Binary(data)
    cur.execute("INSERT INTO images(id, data) VALUES (1, %s)", (binary,) )
    con.commit()
except psycopg2.DatabaseError, e:
    if con:
        con.rollback()
    print 'Error %s' % e    
    sys.exit(1)
finally: 
    if con:
        con.close()

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问题描述

For learning purposes, I'm creating a site using Python+Flask. I want to recover an image from database and show it on screen. But one step at a time.

I have no idea how to save an image in my database in the first place. My searches only revealed that I have to use a bytea type in my database. Then I get my image and somehow (??) convert it to an array of bytes (bytea == array of bites?) and somehow (??) use this array in a insert command.

I was able to discover (maybe) how to do it in Java (here) and C# (here), but I would really like to use Python, at least for now.

Can someone help me?

There are tons of questions of this kind in this site. But most (easily over 85%) of them are replied as "You shouldn't save images in your database, they belong in fs" and fail to answer the question. The rest don't quite solve my problem. So please don't mark this as duplicate if the duplicate has this kind of answer.

推荐答案

I don't normally write complete example programs for people, but you didn't demand it and it's a pretty simple one, so here you go:

#!/usr/bin/env python3

import os
import sys
import psycopg2
import argparse

db_conn_str = "dbname=regress user=craig"

create_table_stm = """
CREATE TABLE files (
    id serial primary key,
    orig_filename text not null,
    file_data bytea not null
)
"""

def main(argv):
    parser = argparse.ArgumentParser()
    parser_action = parser.add_mutually_exclusive_group(required=True)
    parser_action.add_argument("--store", action='store_const', const=True, help="Load an image from the named file and save it in the DB")
    parser_action.add_argument("--fetch", type=int, help="Fetch an image from the DB and store it in the named file, overwriting it if it exists. Takes the database file identifier as an argument.", metavar='42')
    parser.add_argument("filename", help="Name of file to write to / fetch from")

    args = parser.parse_args(argv[1:])

    conn = psycopg2.connect(db_conn_str)
    curs = conn.cursor()

    # Ensure DB structure is present
    curs.execute("SELECT 1 FROM information_schema.tables WHERE table_schema = %s AND table_name = %s", ('public','files'))
    result = curs.fetchall()
    if len(result) == 0:
        curs.execute(create_table_stm)

    # and run the command
    if args.store:
        # Reads the whole file into memory. If you want to avoid that,
        # use large object storage instead of bytea; see the psycopg2
        # and postgresql documentation.
        f = open(args.filename,'rb')

        # The following code works as-is in Python 3.
        #
        # In Python 2, you can't just pass a 'str' directly, as psycopg2
        # will think it's an encoded text string, not raw bytes. You must
        # either use psycopg2.Binary to wrap it, or load the data into a
        # "bytearray" object.
        #
        # so either:
        #
        #   filedata = psycopg2.Binary( f.read() )
        #
        # or
        #
        #   filedata = buffer( f.read() )
        #
        filedata = f.read()
        curs.execute("INSERT INTO files(id, orig_filename, file_data) VALUES (DEFAULT,%s,%s) RETURNING id", (args.filename, filedata))
        returned_id = curs.fetchone()[0]
        f.close()
        conn.commit()
        print("Stored {0} into DB record {1}".format(args.filename, returned_id))

    elif args.fetch is not None:
        # Fetches the file from the DB into memory then writes it out.
        # Same as for store, to avoid that use a large object.
        f = open(args.filename,'wb')
        curs.execute("SELECT file_data, orig_filename FROM files WHERE id = %s", (int(args.fetch),))
        (file_data, orig_filename) = curs.fetchone()

            # In Python 3 this code works as-is.
            # In Python 2, you must get the str from the returned buffer object.
        f.write(file_data)
        f.close()
        print("Fetched {0} into file {1}; original filename was {2}".format(args.fetch, args.filename, orig_filename))

    conn.close()

if __name__ == '__main__':
    main(sys.argv)

Written with Python 3.3. Using Python 2.7 requires that you read the file and convert to a buffer object or use the large object functions. Converting to Python 2.6 and older requires installation of argparse, probably other changes.

You'll want to change the database connection string to something suitable for your system if you're going to test-run it.

If you're working with big images consider using psycopg2's large object support instead of bytea - in particular, lo_import for store, lo_export for writing directly to a file, and the large object read functions for reading small chunks of the image at a time.

其他推荐答案

I hope this will work for you.

import Image
import StringIO
im = Image.open("file_name.jpg") # Getting the Image
fp = StringIO.StringIO()
im.save(fp,"JPEG")
output = fp.getvalue() # The output is 8-bit String.

StringIO Image

其他推荐答案

import psycopg2
import sys

def readImage():
    try:
        fin = open("woman.jpg", "rb")
        img = fin.read()
        return img

    except IOError, e:
        print "Error %d: %s" % (e.args[0],e.args[1])
        sys.exit(1)

    finally:
        if fin:
            fin.close()
try:
    con = psycopg2.connect(database="testdb", user="abc")
    cur = con.cursor()
    data = readImage()
    binary = psycopg2.Binary(data)
    cur.execute("INSERT INTO images(id, data) VALUES (1, %s)", (binary,) )
    con.commit()
except psycopg2.DatabaseError, e:
    if con:
        con.rollback()
    print 'Error %s' % e    
    sys.exit(1)
finally: 
    if con:
        con.close()